Modern plants usually employ grate incineration technologies with "state of the art" flue gas cleaning systems. The waste is tipped into a bunker prior to being fed into the furnace [often after some seperation of materials]. In the furnace the waste is incinerated, producing heat, ash and combustion gasses.

The heat may be recovered in the boiler, producing steam, and then electricity. A plant burning 20,000 tons of waste per annum would expect to produce 11MW of electricity [enough to power around 15,000 homes, if the energy ever gets to the public].

Most of the ash is collected in the ash bunker and then sent on, and is all too often dumped in unsafe landfill or even "reused" in building materials - this "bottom ash" is toxic, as is the "fly ash" from the flue. Indeed the flue gas is even accepted to be highly hazardous by the industry - in the UK this is often sent to landfill, although other European countries cannot legally do this [in fact, they end up shipping it to the UK]. The volume of this waste may be around a tenth of that of the waste that entered, so the volume sent to landfill is less than if the waste went straight to landfill.

The flue gas is cleaned, removing a proportion of the NOx, dioxins and heavy metals, and also much of the dust and acid gas. The idea is to get emissions to below the EU regulation minimum. This is expensive, and gets more so as the regulations tighten. Even so, it is virtually impossible to stay within the regs at all times, and as the regs tighten this too gets more difficult still. Dioxin emissions allowed by the EU are several parts per million below the levels regarded as acceptable in the 1993 draft report of dioxin prepared by the US EPA [Environmental Protection Agency].

The areas of most environmental concern in the two plants above [SELCHP, South-East London & Southampton] would be possible leaching from the Refuse Bunker; failure of the Air Fans; improperly regulated temperatures in the Superheater, Gas Scrubbers and Boiler; spillage or failure in the Filters; spillage within the zones labelled 18-21 above; and chemical formation in the flue gasses as they escape the plant via the stack. The above plant would have a waste & energy flow similar to that of the RDF Facility Processing Line illustrated below. The waste shown is a little disengenuous, as the "clean flue gas" is anything but clean, and therefore should show as part of the waste stream. This is typical of the industry.